This proposal concerns the determinants an} biological role of the bacterial phospholipid (PL) degradation that accompanies the bactericidal action of polymorphonuclear leukocytes (PMN) and of potent membrane-active bactericidal PMN proteins purified in this laboratory. Our specific aims are to examine: (1) The molecular determinants of the action of selective phospholipases A2 against phospholipase A-less mutants of E. coli killed b/ these purified PMN proteins. (2) The determinants of bacterial PL degradation during phagocytosis by PMN isolated from and together with other (soluble) elements in inflammatory exudates. (3) The role of bacterial PL degradation in the overall digestion and structural disorganization of the bacterium. These aims have their origin in our earlier work and their pursuit will therefore rest heavily on well-tested methods used in this laboratory, including: collection of PMN and inflammatory exudates; functional assays of PMN (protein)-bacteria interactions such as phagocytosis, bacterial killing, bacterial PL degradation and biosynthesis; purification and chemical modification of proteins; use of bacterial mutants. Recombinant DNA methods will also be developed to facilitate study of the structural determinants of phospholipase A2 action in bacterial digestion. The long-term objectives of this proposal concern two fundamental questions: (1) What regulates the action of defined intrinsic and exogenous phospholipases on the PL of natural membranes? (2) What determines the extent of digestion of bacteria killed by phagocytes? The proposed studies are likely to provide new insights related to the function of host defenses in infection and of membranes in general.